files - add a method to read content from a position

src/vs/platform/files/common/files.ts

@@ -506,6 +506,12 @@ export interface IResolveContentOptions {
 	 * The optional guessEncoding parameter allows to guess encoding from content of the file.
 	 */
 	autoGuessEncoding?: boolean;
+
+	/**
+	 * Is an integer specifying where to begin reading from in the file. If position is null,
+	 * data will be read from the current file position.
+	 */
+	position?: number;
 }
 
 export interface IUpdateContentOptions {

src/vs/workbench/services/files/node/fileService.ts

@@ -441,10 +441,18 @@ export class FileService implements IFileService {
 					}
 				};
 
+				let currentPosition: number = (options && options.position) || null;
+
 				const readChunk = () => {
-					fs.read(fd, chunkBuffer, 0, chunkBuffer.length, null, (err, bytesRead) => {
+					fs.read(fd, chunkBuffer, 0, chunkBuffer.length, currentPosition, (err, bytesRead) => {
 						totalBytesRead += bytesRead;
 
+						if (typeof currentPosition === 'number') {
+							// if we received a position argument as option we need to ensure that
+							// we advance the position by the number of bytesread
+							currentPosition += bytesRead;
+						}
+
 						if (totalBytesRead > MAX_FILE_SIZE) {
 							// stop when reading too much
 							finish(new FileOperationError(

src/vs/workbench/services/files/test/node/fileService.test.ts

@@ -524,7 +524,7 @@ suite('FileService', () => {
 
 	test('resolveFile', function (done: () => void) {
 		service.resolveFile(uri.file(testDir), { resolveTo: [uri.file(path.join(testDir, 'deep'))] }).done(r => {
-			assert.equal(r.children.length, 7);
+			assert.equal(r.children.length, 8);
 
 			const deep = utils.getByName(r, 'deep');
 			assert.equal(deep.children.length, 4);
@@ -540,7 +540,7 @@ suite('FileService', () => {
 		]).then(res => {
 			const r1 = res[0].stat;
 
-			assert.equal(r1.children.length, 7);
+			assert.equal(r1.children.length, 8);
 
 			const deep = utils.getByName(r1, 'deep');
 			assert.equal(deep.children.length, 4);
@@ -879,4 +879,22 @@ suite('FileService', () => {
 			});
 		});
 	});
+
+	test('resolveContent - from position (ASCII)', function (done: () => void) {
+		const resource = uri.file(path.join(testDir, 'small.txt'));
+
+		service.resolveContent(resource, { position: 6 }).done(content => {
+			assert.equal(content.value, 'File');
+			done();
+		}, error => onError(error, done));
+	});
+
+	test('resolveContent - from position (with umlaut)', function (done: () => void) {
+		const resource = uri.file(path.join(testDir, 'small_umlaut.txt'));
+
+		service.resolveContent(resource, { position: new Buffer('Small File with Ü').length }).done(content => {
+			assert.equal(content.value, 'mlaut');
+			done();
+		}, error => onError(error, done));
+	});
 });

src/vs/workbench/services/files/test/node/fixtures/service/small_umlaut.txt

+Small File with Ümlaut
\ No newline at end of file